As electronic circuits continue to become smaller, operate at higher frequencies, and are widely applied in unprotected environments, it has become easier to either completely destroy or otherwise impair electronic components therein by application of voltages beyond component ratings. In particular, many integrated circuits and semiconductor devices are highly susceptible to damage from the unintended discharge of static electricity, generally as a result of handling or from physical contact with another charged body, or from electrical overstress. Electrostatic discharge is the transfer of an electric charge between bodies at different electrostatic potentials (voltages), caused by direct contact, or induced by an electrostatic field. Electrical overstress generally refers to the occurrence of a transient voltage, and even a steady voltage such as due to a component failure, in a circuit above its rated operating voltage. These events have become a critical problem for the electronics industry.
Device failures that result from ESD events are not always immediately catastrophic or apparent. Often, the device is only slightly weakened but is less able to withstand normal operating stresses and, hence, may result in a reliability problem or a reduced lifetime. Therefore, various ESD protection circuits should be included in the device to protect its various components.
When an ESD discharge or an EOS (electrical overstress) event is coupled to a transistor or other semiconductor element, the high, pulsed voltage and current relative to the voltage- and current-sustaining capabilities of structures within the device can break down the transistor, and potentially cause latent or permanent damage. Consequently, circuits associated with input/output pads of an integrated circuit generally require protection from ESD pulses, and EOS events in general, so that they are not damaged by such occurrences.
Devices for ESD protection must be designed to carry a high current while clamping the voltage below the destruction voltage of a functional device and circuit during an ESD pulse. This requirement generates a need for ESD protection devices of substantial physical size in order to provide low series resistance for an ESD pulse to be clamped. The occurrence of voltages higher than an originally intended value can lead to ESD failures within the functional circuitry.
A number of ESD circuit design approaches for circuits that operate in a high-frequency regime have been proposed, but these often provide inadequate ESD protection for an electronic circuit that may be rated at a maximum voltage of only several volts, that may operate in a frequency regime that may be substantially higher than 10 GHz, and that is amenable to the low-cost demands of a high volume, competitive market.
Thus, there is a need for an ESD protection device capable of providing a sufficiently low impedance to ground for an ESD pulse without concurrent impedance loading of a node to be protected, and without substantial added product cost, thereby economically preventing failure of circuits and products due to ESD events.